Field associate Pippa Halverson from Harvard University
with his hand on a knife-sharp flooding surface representing an end to
a ca. 720 million-year-old ice age in the Otavi Group of Namibia.
Below his hand are boulder sized granite and carbonate dropstones from
the glaciomarine Ghaub Formation. Above are finely laminated, fine-grained
dolomicrites of the Maieberg Formation, likely deposited very rapidly as
the glaciers melted and sealevel rose.
Secular variations in the carbon-isotopic compositions
of inorganic carbonate and co-existing organic carbon. The significantly
reduced fractionation in the cap carbonates immediately above and below
the glaciations suggests carbon limitations to growing photosynthetic microorganisms.